Method for refining molten glass

ABSTRACT

A method of removing undesirable gaseous inclusions, also known as seeds and bubbles, from seed containing or unrefined molten glass by continuously introducing this unrefined molten glass into a rapidly rotating contained glass mass, subjecting the unrefined molten glass mass to centrifugal forces substantially greater than gravity, and developing static pressure differences in the glass mass, resulting in pressure gradients in the molten glass and causing the gaseous inclusions to migrate to areas of lower static pressure and to the atmosphere from the molten glass, and subjecting the partially refined molten glass to increased centrifugal forces to remove additional gaseous inclusions, delivering refined molten glass from the contained glass mass, having reduced numbers of gaseous inclusions. The refining apparatus is a container for holding molten glass mounted for rotation about its axis of rotation. A refractorylined chamber within the container holds molten glass; the container has a centrally located top inlet, and a centrally located outlet at the bottom of the container. A slinger plate is positioned near the top inlet for diverting the entering molten glass stream within the container. A diverter plate is positioned within the container near the outlet of the container and causes the molten glass to flow adjacent the chamber wall on the way to the discharge, then subjecting the molten glass to an increased centrifugal force, and increasing the number of gaseous inclusions removed from the molten glass. The container has a flange, encircling the outside thereof. Pair of rotatable driving wheels support the flange and provide means for rotating the container.

United States Patent [191 Richards et al.

[ METHOD FOR REFINING MOLTEN GLASS [75] inventors: Raymond S. Richards;Robert R.

Rough; Douglas F. St. John, all of Toledo, Ohio 52 US. Cl. 65/134,65/178, 65/180,

' 55/36, 55/400 [51] Int. Cl C031) 5/18 [58] Field of Search 65/134,178, 180;

[56] References Cited UNlTED STATES PATENTS 2,006,947 7/1935 Ferguson65/1 34 2,007,755 7/1935 Ferguson 65/134 2,493,260 l/1950 Paquette et al65/134 2,871,000 l/1959 Dowling 65/180 2,138,468 1 li/1938 Ayres 233/182,587,206 2/1952 Pattinson 233/47 R 2,222,727 11/1940 Stigen 233/222,113,963 4/1938 Morton 65/178 Primary Examiner-S. Leon BashoreAssistant Examiner-Kenneth M. Schor Attorney-E. F. Dwyer and E. J.Holler [57] ABSTRACT A method of removing undesirable gaseousinclusions,

[451 Aug. 28, 1973 also known as seeds and bubbles, from seed containingor unrefined molten glass by continuously introducing this unrefinedmolten glass into a rapidly rotating contained glass mass, subjectingthe unrefined molten glass mass to centrifugal forces substantiallygreater than gravity, and developing static pressure differences in theglass mass, resulting in pressure gradients in the molten glass andcausing the gaseous inclusions to migrate to areas of lower staticpressure and to the atmosphere from the molten glass, and subjecting thepar-' tially refined molten glass to increased centrifugal forces toremove additional gaseous inclusions, delivering refined molten glassfrom the contained glass mass, having reduced numbers of gaseousinclusions.

The refining apparatus is a container for holding molten glass mountedfor rotation about its axis of rotation. A refractory-lined chamberwithin the container holds molten glass; the container has a centrallylocated top inlet, and a centrally located outlet at the bottom of thecontainer. A slinger plate is positioned near the top inlet fordiverting the entering molten glass stream within the container. Adiverter plate is positioned within the container near the outlet of thecontainer and causes the molten glass to flow adjacent the chamber wallon the way to the discharge, then subjecting the molten glass to anincreased centrifugal force, and increasing the number of gaseousinclusions removed from the molten glass.

The container has a flange, encircling the outside thereof. Pair ofrotatable driving wheels support the flange and provide means forrotating the container.

29 Claims, 6 Drawing Figures PAIENIEDmza nan SHEUGBFG 1 METHOD FORREFINING MOLTEN GLASS BACKGROUND OF THE INVENTION Field of the InventionThis invention relates to a method and apparatus for refining moltenglass to remove entrapped gaseous inclusions.

Gaseous Inclusion Sizing Such gaseous inclusions are described in theart as seeds or blisters. The large seeds are designated blisters;however, there is no sharp line or demarcation between theclassification of seeds and blisters. Seeds generally fall into therange of 0.001 inch to 0.030 inch diameter. This invention removesgaseous inclusions or seeds most effectively when the seeds are in therange of 0.001 inch to 0.030 inch and upwards in diameter.

DESCRIPTION OF THE PRIOR ART One method of removing gaseous inclusionsor refining glass in the prior art is to separately mix and then meltand heat the glass in the same or contiguous chambers to remove gaseousinclusions, resulting in essentially simultaneous melting and gaseousinclusion removal. Glass is made in this prior art way by meltingglass-forming sand and stabilizing oxides at high temperatures in arefractory-lined tank to form molten glass. Sand and the otherglass-forming constituent materials are accurately proportioned to yieldglass of the desired composition, mixed, with or without adding heat, sothat the material will be homogeneous, and the batch materials areheated to a sufficiently high temperature until the batch becomes amolten glass bath. Chemical reactions during the heating lead to thegeneration of bubbles or gaseous inclusions. These gaseousinclusions arethen removed by continuing the heating of the molten glass in the tank.The heating time required for the elimination of the gaseous inclusionsis further reduced, by the addition of fining agents, which facilitatethe ultimate removal of gaseous inclusions during the continued heatingof the molten glass.

Such prior art refining processes may also utilize physical agitation ofthe molten glass, bubbling gas through the molten glass ormechanicallyagitating the batch to decrease the time required forremoving gaseous inclusions.

The refining process and apparatus of this invention can remove gaseousinclusions from unrefined molten glass in practically unlimited numbers.

Other prior art attempts to melt and refine glass are disclosed in U.S.Pat. No. 2,006,947 to J. Ferguson, issued July 2, 1935; and U.S. Pat.No. 2,007,755, to J. Ferguson, issued July 9, I935.

The Ferguson U.S. Pat. No. 2,006,947 discloses an apparatus whereinbatch materials are fed to a vertical furnace, rotating at a relativelyslow speed; and heat is applied to the furnace to melt the batchmaterial and form a thin layer of molten glass on the inner surface ofthe furnace. The rotation of the furnace produces centrifugal force onthe thin layer of glass, which tends to remove seeds from the moltenglass.

SUMMARY OF THE INVENTION This invention relates to a method andapparatus for refining molten glass by supplying unrefined molten glass,i.e., having a high gaseous inclusion count, rotating a confined mass ofsuch glass to produce an essentially paraboloidal void therein, causedby the rotation of the molten glass, and establishing areas of higherpressure and areas of lower pressure, which result in pressure gradientswithin the rotating glass mass and causing the gaseous inclusions totravel from areas of high static pressure to areas of lower staticpressure and then from the molten glass to the void; and continuallywithdrawing the refined molten glass from the rotating glass mass. Theprocess provides a refined molten glass with a lowered gaseous inclusioncontent. The refining operation of this invention eliminates the needfor prolonged heating of large baths of molten glass, over long periodsof time, to remove gaseous inclusions; can eliminate'a need for theaddition of fining agents, and reduces the residence time of the moltenglass in the refining operation, thereby reducing costs and minimizinginterface reactions, one of the sources of gaseous inclusions. Theapparatus of the invention is a container having a refractory-linedchamber and which is mounted for rotation about its central verticalaxis; a slinger plate is positioned within the chamber, near the glassentrance point. A diverter plate is positioned within the chamber, belowthe paraboloid void and nearer the discharge of the rotating container.The diverter plate diverts partially refined molten glass to areas ofincreased centrifugal force, near the chamber walls, redirecting asubstantial portion of the remaining gaseous inclusions to the void, andfurther refines the molten glass.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view, in partialcross-section, of the apparatus of this invention;

FIG. 2 is a sectional view from the top of the slinger plate; along line22 of FIG. 1;

FIG. 3 is a sectional view from the top of the diverter plate; alongline 33 of FIG. 1;

FIG. 4 is a perspective view of the refining apparatus showing thestabilizing wheels;

FIG. 5 is a schematic representation of the apparatus showing multipleprocessing zones;

FIG. 6 is a graph showing the relationship between a process variablecondition such as glass output in tonsper-day, versus seedcount-per-ounce of the refined glass using the apparatus of Example I.

GENERAL DESCRIPTION OF THE INVENTION In the practice of this invention,previously mixed and melted materials, produce unrefined molten glasshaving a high density of gaseous inclusions; this unrefined glass issubsequently introduced into the upper end of a continuously rotatingchamber of the refining apparatus. The chamber contains a sufficientlylarge mass of glass to produce a paraboloidal void in the glass, whenrotated. Continuous rotation of the chamber about its axis subjectsportions of the mass of glass in the chamber to centrifugal force and,thereby, causes generally radially extending pressure gradients withinthe molten glass, which causes the gaseous inclusions to migrate to theparaboloidal cavity. The refined molten glass is continuously removedfrom the lower end of the chamber at a rate substantially correspondingto the rate at which the unrefined molten glass is introduced into thechamber.

In one preferred form of the invention, the entering stream of unrefinedmolten glass is directed radially outward toward the sides of thechamber. In addition, portions of the molten glass from below theparaboloidal void, are redirected radially outwardly toward theperiphery of the chamber to move these portions to an area of greatercentrifugal force, to further facilitate the removal of the gaseousinclusions before the refined molten glass is removed from the lower endof the chamber, as will be described in detail hereinafter.

' APPARATUS Referring to FIG. 1, the apparatus for removing gaseousinclusions 22 from molten glass mass 21 comprises a container whichincludes a cylinder 11, layers 12 of refractory material and insulatingmaterials 13 positioned within the cylinder and forming a chamber 35 forholding molten glass and reducing heat losses. The container is mountedfor rotation about its vertical axis. The axis of rotation may be tiltedaway from the vertical over a range toward the horizontal, but the axisof rotation is preferably more vertical than horizontal.

The container has an inlet section 14 and a discharge section 15. Theinlet is centered in the top of the container. The discharge section 15is centered in the bottom of the container.

The inlet 14 has narrow inlet opening portion 26, which is smaller indiameter than the chamber 35.

A slinger plate 30 is positioned in proximity to the inlet 14 anddiverts unrefined molten glass from an entering axial path radiallytoward the inner surface of the refractory chamber 35. The slinger plate30 is anchored in the refractory lining (FIG. 1).

The slinger plate 30, as shown in a top view (FIG. 2), has two rows ofcircumferentially-spaced, substantially identical slots 31, throughwhich the unrefined molten glass passes into the chamber, and gaseousmaterial passes out from the chamber and out of the container.

The total cross-sectional area of the slots 31 of the slinger plate 30is such that there is relative unimpeded flow of the unrefined moltenglass through the slinger plate 30. The slinger plate 30 diverts theaxial flow of unrefined molten glass and causes the flow to changedirection in the chamber to a generally radially outward direction, fromthe axial.

A diverter plate 16 (FIG. 1) is positioned generally horizontal near thedischarge section 15 of the container. The diverter plate 16 in thisembodiment is anchored in the refractory liner 12. FIG. 3 shows a topview of the diverter plate 16. The plate 16 is provided with a pluralityof passages, which can be uniformly spaced; substantially identicalslots 25, adjacent to the outerperiphery of the plate, adjacent thechamber walls, which provide a passage for the molten glass to thedischarge tube 27 of the chamber.

The diverter plate 16 directs the molten glass toward the periphery ofthe inner wall of the chamber 35, into areas of increased centrifugalforce, compared with the centrifugal force radially inward from thewall. The increased centrifugal force tends to increase the number ofgaseous inclusions directed to the paraboloidal void 23, formed in theglass, due to rotation, and removes additional numbers of gaseousinclusions from the molten glass in the chamber.

Discharge tube 27 is provided in the chamber bottom, and it is smallerin diameter than the bottom diameter of chamber 35. One end of dischargetube 27 extends beyond the lower surface of the chamber bottom into thedischarge section 15 of the container.

A glass-collecting rod 20 is positioned by any suitable means adjacentthe discharge conduit 27, to collect the exiting molten glass.

A flange 17, for supporting the container, encircles the outer peripheryof the cylinder 11 the glasscollecting rod provides a discharge pathfrom the chamber to any glass-collecting means. Rotatable drive wheels18 and 19 engage the under-surface of the flange and support thecontainer. One of the wheels is driven by a drive shaft 24, from aconventional motive power, such as an electric motor (not shown), the

driven wheel 18 engaging a surface of the flange l7, rotates thecontainer. FIG. 4 illustrates the stabilizing wheels used formaintaining the rotating container generally in its axis of rotation.

Rotatable wheels 33 and 34 are positioned about the outer surface of thecontainer, near the top and bottom thereof, to stabilize the containerwhile rotating (FIG. 4).

Chamber 35 has the outer configuration of an elongated cylinder, thechamber 35 having a radius which is substantially constant from the topto the bottom thereof, especially in the portions which form the moltenglass holding chamber.

The outer configuration of the molten glass mass 21 is controlled by theshape of the container. In the cylindrical form of FIG. 1, the mass ofglass is controlled to subject the mass of glass to the same centrifugalforce, along any line equi-distant and parallel to the central verticalaxis.

In embodiments wherein the container holds the mo]- ten glass, without arefractory chamber, the same configuration as described for the chamber,may be used, and the above description is equally applicable to thecontainer.

Other configurations may be used, such as one wherein the radius of alower portion of the chamber is greater than the radius of an adjacentupper portion of the chamber.

METHOD Removing entrapped gaseous inclusions, known also in the art asseeds and bubbles, is performed by introducing unrefined molten glassinto a rapidly rotating container, providing a contained rotating glassmass therein, forming in the molten glass a substantially paraboloidalvoid communicating with the atmosphere. The rotation of the glass masssubjects the unrefined molten glass to centrifugal forces substantiallygreater than gravity and develops static pressure differences throughoutthe glass mass, resulting in pressure gradients in the molten glass.There, pressure gradients provide a moving force causing the gaseousinclusions to travel from areas of higher static pressure to areas oflower static pressure, sending a large number of the gaseous inclusionsinto the void, and delivering molten glass from the contained rotatingglass mass, having both reduced numbers of gaseous inclusions andsmaller sized gaseous inclusions.

Pressure gradients cause gaseous inclusions to move generally along thepressure gradients from points of higher pressure to points of lowerstatic pressure, but the direction of travel of any gaseous inclusion isa vector resultant of forces acting on the gaseous inclusions; however,those gaseous inclusions which do not enter the void remain in themolten glass and flow to an area of molten glass which is beneath theapex of the void.

The diverter plate 16 positioned beneath the apex of the void directsthe molten glass into an area of increased centrifugal force as it flowsto the discharge. The increased centrifugal force redirects some of thegaseous inclusions remaining in the glass toward and into the void,removing most gaseous inclusions in the size range of 0.001 inch to0.010 inch and upwards from the molten glass, and further refining theglass. Gaseous inclusions in the size range smaller than about 0.001inch do not go into void, but pass out of the refiner in the refinedmolten glass; smaller sizes can be removed with a change in operation ofthe apparatus; or process parameters.

FIG. 5 shows multiple zones of processing in the rotating glass massdesignated as zones A, B and C. The A zone is a zone of rotating moltenglass developing therein a paraboloidal void. The C" zone includes thearea above the diverter plate and the area of molten glass influenced bythe diverter; the B zone is the area of molten glass lying between theupper boundary of influence of the diverter on the flow of the moltenglass, and below the tip of the void. A detailed description of theprocessing zones follows hereinbelow.

In one practice of this invention, glass-making materials are placedinto a melting apparatus (not shown), and mixed to homogenize the batchmaterial, and the mixture of batch materials is raised to above themelting point of the batch material to produce molten unrefined glasshaving great numbers of undesirable gaseous inclusions. The unrefinedmolten glass is then transferred from the melting apparatus to thecontainer either as a continuous or an intermittent stream. Thecontainer rotates and the molten glass mass is thus rotated and developsa void, as shown in zone A (FIG. 5).

The rotating void has a surface with portions which are steeply inclinedto the vertical. The angle of this surface inclination is determined bythe speed of rotation and the distance of that point on the surface fromthe apex of the paraboloidal void, wherein the inclina tion angle ismeasured. The distance from the apex of the void, to the bottom of thecontainer, is determined by the volume of the glass within the rotatingcontainer, at any selected R.P.M.

The glass mass surrounding the void has an increasing thicknessdownward, as measured along any axially extending line. Centrifugalforces in the glass at the chamber wall and centrifugal forces on theinnermost portion of glass at the void, differ, and the differenceincreases as the glass mass progresses, from the upper end of thechamber toward the bottom of the void, measured along any radiallyextending line, from the axis to the wall.

The path of travel of any gaseous inclusion is a vector resultant of theforces acting on it. Forces which act upon gaseous inclusions in the "A"zone includes centrifugal force produced by the rotation of the glassmass, the force resulting from the velocity of the downward flow of theviscous molten glass through the container, and a buoyant force of thegaseous inclusion in the molten glass.

When the centrifugal forces are sufficiently greater than other forcesacting on the gaseous inclusion, to cause a favorable vector resultantforce, the path of travel for most gaseous inclusions is generallytoward the void, unless the combination of downward glass velocitydistance to the void, and time, does not permit travel to the void.

The vector resultant force on the gaseous inclusion in zone A" isinfluenced by the size of the gaseous inclusion, the viscosity of themolten glass, the density of the molten glass, gravitational force,centrifugal force, and the velocity of the downward flow of the moltenglass in the apparatus. These forces interact to produce a vectorresultant force that determines whether a particular bubble is removedfrom the glass via the void or remains in the glass and goes into zone8" area below the apex of the void; these gaseous inclusions aredesignated bypass inclusions".

This invention provides means and method to recapture and redirect thesebypass inclusions by restructuring the vector resultant force actingupon some of the bubbles in zone C" and send a percentage of the bypass"bubbles, to the void, through zone B. The means is a diverter plate 16positioned in zone C," between the apex of the void and the discharge27. The diverter causes all of the molten glass in zone B to passthrough an area of greater centrifugal force at the periphery of zone C.This increased centrifugal force changes the vector resultant force onsome of the bubbles and, in some cases, causes gaseous inclusions totravel back into zone B and toward the paraboloidal void. The recapture"action of the diverter results in the removal of more gaseous inclusionsfrom the molten glass than would be removed by the process operatingwithout the diverter plate 16.

Those gaseous inclusions not removed by this diversion activity passthrough with the molten glass into the discharge of the apparatus.

This invention removes gaseous inclusions rapidly compared with theprior art glass bath thermal refining of up to 36 hours or more; thenumber of gaseous inclusions is reduced to about 500 600seeds-per-ounce, within an hour, and usually within an average residencetime of about 15 minutes or less for any retained mass of glass. Thenumber and sizes of gaseous inclusions remaining, decreases with anincrease in residence time of a retained mass of glass.

EXAMPLE I in preparing example I, unrefined glass batch was preparedusing a sand, soda ash, limestone, feldspar mix and melted in a rotaryfurnace to a temperature of above 2,600F., and the unrefined glass had agaseous inclusion or seed count of about 20,000 to 40,000 seeds perounce; the unrefined molten glass was delivered to a rotating container10 at about 2,600F. The container 10 in example I had an overall heightof approximately 48 inches, outside diameter of approximately 24 inches,and a chamber diameter of 6 inches. The container was rotated at a speedof approximately 970 revolutions-per-minute. At this speed, a paraboloiddeveloped with a diameter of approximately 2.5 inches at a void heightof about 20 inches, with a molten glass depth of approximately 15 inchesfrom the tip of the void 23 to the chamber bottom.

The rotation of the container at about 970 RPM produces a centrifugalforce near the internal surface of the chamber of about times the forceof gravity.

The surface of the paraboloidal void has portions which are steeplyinclined to the horizontal. The inclination angle of this surface isdetermined by the speed of rotation and the distance of the surfacepoint being measured'from the apexof the paraboloidal void; for example,at about 970 RPM, a line drawn tangent to the point 12 inches up fromthe apex of paraboloidal void, and intersecting a horizontal plane, hasan inclination from the horizontal line of 87.8".

The apparatus refined molten glass at the rate of about 5.0 tons per24-hour day and produced glass having about 500 seeds-per-ounce usingthe method of counting seeds described herein below.

The method of determining seeds-per-unit volume is based upon a visualcount of seeds-per-ounce of glass when the glass is obliquely lit andimmersed under a liquid with a similar refractional index, such asmonochloro-benzene.

The size of seeds can'be determined with the use of a reticle orgradient in conjunction with a magnifying lens or by automaticdifferential area determination techniques known to those skilled in theart.

FIG. 6 is a graph of the data of Example I, showing the'relationshipbetween flow (output) in tons-per-24- hour day, and approximate seedcount in seeds-perounce of glass refined.

The molten glass was maintained at about its entering temperaturethroughout the process, and the exiting stream of refined glass was nearthe temperature of the entering stream.

Table I, in addition to'Example I, shows four other examples of seedremoval using this invention.

The entering and exiting temperatures were measured using an opticalpyrometer.

The parabola diameter was measured at its greatest axial diameter, atthe heights indicated, measured along the axis of rotation from the tipof the void.

The result of all factors, RPM, viscosity, and throughput, on thepercentage of gaseous inclusions removed in any size range, isdesignated the Refining Factor.

The Refining Factor can be increased in the operation of the apparatusof Example 1 by increasing the number of RPM, temperature, residencetime of the retained mass, either singly or in combination, or changingthe parameters of the apparatus.

This ability to effect meaningful changes in the Refining Factor"provides a refining process with a high degree of flexibility inchoosing operating conditions to determine the ultimate seed count ofthe refined glass.

The maximum Refining Factor" for any set of selected operatingconditions, i.e., Example I, is achieved when the paraboloidal void isapproximate in length to the depth of the molten glass beneath the tipof the void to the bottom of the chamber.

This invention also provides a method and apparatus ing mass of moltenglass to a void produced in the glass 7 mass by centrifugal forceinduced by the rotation of the mass, and in the absence of finingagents, if desired,

and wherein the refining is accomplished without the.

addition of heat to the glass during the refining operation.

OTHER EMBODIMENTS The apparatus (FIG. I) of this invention canbe-operated without the diverter 16; the Refining Factor" is greatlyreduced; this reduction in refining factor reduces the number of gaseousinclusions removed using, for example, the operating conditionsequivalent to Example l.

We claim:

l. The method of refining molten glass which comprises:

defining a chamber having an axis of rotation and which has a restrictedlower end forming an outlet; introducing molten glass whereinsubstantially all the glass constituents are molten and which containsentrapped gaseous inclusions into the chamber providing a mass of moltenglass in the chamber; rotating said chamber about its axis to subjectportions of the mass of glass in the chamber to centrifugal force;controlling the configuration of the chamber, the speed of rotation ofthe chamber, and the amount of glass in the chamber, such that at leasta portion of the mass of glass in the chamber forms a substantiallycylindrical portion with a paraboloidal void, said substantiallycylindrical portion of glass extending from the top of the mass of glassin the chamber to the apex of the paraboloidal void having a radialthickness which increases progressively from the top "to the apex of theparaboloidal void;

adding unrefined molten glass to the chamber to maintain the mass ofglass in the chamber substantially constant; and

substantially continuously removing refined molten glass from the lowerend of the chamber to maintain said mass of glass in said chambersubstantially constant.

2. The method set forth in claim ll wherein the step of controlling theconfiguration of the chamber, the speed of rotation of the chamber, andthe amount of glass in the chamber is such that the mass of glass in thechamber increases in radial width from the top of the mass of the glassto the apex of the paraboloidal void.

3. The method set forth in claim 1 wherein the step of controlling theconfiguration of the chamber, the speed of rotation of the chamber, andthe amount of glass in the chamber is such that the average axialvelocity of the glass does not increase from the top of the mass ofglass to the apex of the paraboloidal void.

4. The method'set forth in claim ll, including the step of controllingthe amount of molten glass in the chamber such that there is asubstantial mass of glass between the apex of the paraboloidal void andthe outlet of the chamber.

5. The method set forth in claim 4, including the step of redirectingthe molten glass beneath the apex of the paraboloidal void, so that themolten glass in the area between the void and the outlet is caused tomove radially outward toward the wall of the chamber in advance of theoutlet.

6. The method set forth in claim 4, including the step of redirectingthe molten glass beneath the apex of the 9 paraboloidal void such thatit is caused to move through a path adjacent the wall of the chamberbefore moving to the outlet.

7. The method set forth in claim 4, including the step of causing themolten glass between the apex of the paraboloidal void and the outlet tomove radially outward from its apex of rotation and then generallyradially inward to move portions of the molten glass through an area ofcentrifugal pressure greater than the pressure in the area at the axisof its rotation.

8. The method set forth in claim 1, including the step of controllingthe speed of rotation of the chamber such that the height of theparaboloidal void formed in the molten glass is at least several timesthe maximum diameter of the paraboloidal void.

9, The method set forth in claim 1, wherein the step of controlling theamount of molten glass in the chamber is such that the radial thicknessof the glass at the upper end of the chamber exceeds the radius of theparaboloidal void in the glass at the upper end of the chamber.

10. The method set forth in claim 1, wherein the step of introducing themolten glass into the chamber comprises directing the glass laterallysuch that molten glass merges with the mass of glass in the chamberadjacent the upper end of the chamber.

11. The method set forth in claim 1, wherein the step of controlling theamount of molten glass in the chamber is such that the height of theparaboloidal void is about equal to the depth of the glass beneath theapex of the paraboloidal void.

12. The method set forth in claim 1, including the step of controllingthe configuration of the chamber such that it has a substantiallyconstant diameter from the upper end to the lower end thereof.

13. The method set forth in claim 1, including the step of causing themolten glass between the apex of the paraboloidal void and the outlet tomove radially outward from its axis of rotation and then generallyradially inward to move portions of the molten glass through an area ofcentrifugal pressure greater than the pressure in the area at the axisof its rotation.

14. The method of refining molten glass which comprises:

defining a substantially cylindrical chamber having an axis of rotationand which has an upper end and a restricted lower end forming an outlet;

introducing molten glass wherein substantially all the glassconstituents are molten and which contains entrapped gaseous inclusionsinto the open upper end of the chamber providing a mass of molten glassin the chamber;

rotating said chamber about its axis to subject portions of the mass ofglass in the chamber to centrifugal force;

controlling the configuration of the chamber, the

speed of rotation of the chamber, and the amount of glass in the chambersuch that the mass of glass in the chamber forms a paraboloidal voidhaving a top and an apex, and the glass mass has a radial thicknesswhich increases progressively from the top to the apex of the void;

adding unrefined molten glass to the upper end of the chamber tomaintain the mass of glass in the chamber substantially constant; and

substantially continuously removing refined molten glass from the lowerend of the chamber to maintain the mass of said glass substantiallyconstant.

15. The method set forth in claim 14 wherein the step of controlling theconfiguration of the chamber, the speed of rotation of the chamber, andthe amount of glass in the chamber is such that the average axial ve'locity of the glass does not increase from the top of the mass of glassto the apex of the paraboloidal void.

16. The method set forth in claim 14, including the step of controllingthe amount of molten glass in the chamber such that there is asubstantial mass of glass between the apex of the paraboloidal void andthe outlet of the chamber.

17. The method set forth in claim 16, including the step of redirectingthe molten glass beneath the apex of the paraboloidal void so that themolten glass in the area between the void and the outlet is caused tomove radially outward toward the wall of the chamber in advance of theoutlet.

18. The method set forth in claim 16, including the step of redirectingthe molten glass beneath the apex of the paraboloidalvoid such that itis caused to move through a path adjacent the wall of the chamber beforemoving to the outlet.

19. The method set forth in claim 16, including the step of causing themolten glass between the apex of the paraboloid void and the outlet tomove radially outward from its axis of rotation and then generallyradially inward to move portions of the molten glass through an area ofcentrifugal pressure greater than the pressure in the area at the axisof its rotation.

20. The method set forth in claim 14, including the step of controllingthe speed of rotation of the-chamber such that the height of theparaboloidal void formed in the molten glass is at least several timesthe maximum diameter of the paraboloidal void.

21. The method set forth in claim 14, wherein the step of controllingthe amount of molten glass in the chamber is such that the radialthickness of the glass at the upper end of the chamber exceeds theradius of the paraboloidal void in the glass at the upper end of thechamber.

22. The method set forth in claim 14, wherein the step of introducingmolten glass comprises directing the glass into the open upper end ofthe chamber laterally such that molten glass merges with the mass ofglass in the chamber adjacent the upper end of the chamber.

23. The method set forth in claim 14, wherein the step of controllingthe amount of molten glass in the chamber is such that the height of theparaboloidal void is about equal to the depth of glass beneath the apexof the paraboloidal void.

24. The method set forth in claim 14, including the step of controllingthe configuration of the chamber such that it has a substantiallyconstant diameter from the upper end to the lower end thereof.

25. The method set forth in claim 14, including the step of causing themolten glass between the apex of the paraboloidal void and the outlet tomove radially outward from its axis of rotation and then generallyradially inward to move portions of the molten glass through an area ofcentrifugal pressure greater than the pressure in the area at the axisof its rotation.

26. The method of refining molten glass which comprises:

defining a chamber having an axis of rotation; rotating said chamberabout said axis; introducing molten glass, wherein substantially all theglass constituents are molten and which contains entrapped gaseousinclusions into the chamber providing a mass of molten glass in thechamber; continuing the rotating of said chamber about its axis tosubject portions of the mass of glass in the chamber to centrifugalforce, and thereby cause the mass of glass to form a portion of aparaboloidal void under the action of the centrifugal force; andcontrolling the configuration of the chamber, the speed of rotation ofthe chamber, and the amount of glass in the chamber such that at least aportion of the mass of glass in the chamber forms a substantiallycylindrical portion with a paraboloidal void, said substantiallycylindrical portion of glass extending from the top of the mass of glassin the chamber to the apex of the paraboloidal void, and

having a radial thickness which increases progres the upper end to thelower end thereof.

29. The method of refining molten glass which comprises:

rotating said chamber about its axis to subject portions of the mass ofglass in the chamber to centrifugal force;

controlling the configuration of the chamber, the speed of rotation ofthe chamber, and the amount of glass in the chamber such that aparaboloidal void is formed in the mass of glass;

adding unrefined molten glass to the upper end of the chamber tomaintain the mass of glass in the chamber substantially constant; and

substantially continuously removing molten glass from the lower end ofthe chamber; and

causing the molten glass between the apex of the paraboloidal void andthe outlet to move radially outward from its axis of rotation and thengenerally radially inward to move portions of the molten glass into thearea of centrifugal pressure greater than the pressure in the area atthe axis of its rotation.

t 8 i i i

2. The method set forth in claim 1 wherein the step of controlling theconfiguration of the chamber, the speed of rotation of the chamber, andthe amount of glass in the chamber is such that the mass of glass in thechamber increases in radial width from the top of the mass of the glassto the apex of the paraboloidal void.
 3. The method set forth in claim 1wherein the step of controlling the configuration of the chamber, thespeed of rotation of the chamber, and the amount of glass in thE chamberis such that the average axial velocity of the glass does not increasefrom the top of the mass of glass to the apex of the paraboloidal void.4. The method set forth in claim 1, including the step of controllingthe amount of molten glass in the chamber such that there is asubstantial mass of glass between the apex of the paraboloidal void andthe outlet of the chamber.
 5. The method set forth in claim 4, includingthe step of redirecting the molten glass beneath the apex of theparaboloidal void, so that the molten glass in the area between the voidand the outlet is caused to move radially outward toward the wall of thechamber in advance of the outlet.
 6. The method set forth in claim 4,including the step of redirecting the molten glass beneath the apex ofthe paraboloidal void such that it is caused to move through a pathadjacent the wall of the chamber before moving to the outlet.
 7. Themethod set forth in claim 4, including the step of causing the moltenglass between the apex of the paraboloidal void and the outlet to moveradially outward from its apex of rotation and then generally radiallyinward to move portions of the molten glass through an area ofcentrifugal pressure greater than the pressure in the area at the axisof its rotation.
 8. The method set forth in claim 1, including the stepof controlling the speed of rotation of the chamber such that the heightof the paraboloidal void formed in the molten glass is at least severaltimes the maximum diameter of the paraboloidal void.
 9. The method setforth in claim 1, wherein the step of controlling the amount of moltenglass in the chamber is such that the radial thickness of the glass atthe upper end of the chamber exceeds the radius of the paraboloidal voidin the glass at the upper end of the chamber.
 10. The method set forthin claim 1, wherein the step of introducing the molten glass into thechamber comprises directing the glass laterally such that molten glassmerges with the mass of glass in the chamber adjacent the upper end ofthe chamber.
 11. The method set forth in claim 1, wherein the step ofcontrolling the amount of molten glass in the chamber is such that theheight of the paraboloidal void is about equal to the depth of the glassbeneath the apex of the paraboloidal void.
 12. The method set forth inclaim 1, including the step of controlling the configuration of thechamber such that it has a substantially constant diameter from theupper end to the lower end thereof.
 13. The method set forth in claim 1,including the step of causing the molten glass between the apex of theparaboloidal void and the outlet to move radially outward from its axisof rotation and then generally radially inward to move portions of themolten glass through an area of centrifugal pressure greater than thepressure in the area at the axis of its rotation.
 14. The method ofrefining molten glass which comprises: defining a substantiallycylindrical chamber having an axis of rotation and which has an upperend and a restricted lower end forming an outlet; introducing moltenglass wherein substantially all the glass constituents are molten andwhich contains entrapped gaseous inclusions into the open upper end ofthe chamber providing a mass of molten glass in the chamber; rotatingsaid chamber about its axis to subject portions of the mass of glass inthe chamber to centrifugal force; controlling the configuration of thechamber, the speed of rotation of the chamber, and the amount of glassin the chamber such that the mass of glass in the chamber forms aparaboloidal void having a top and an apex, and the glass mass has aradial thickness which increases progressively from the top to the apexof the void; adding unrefined molten glass to the upper end of thechamber to maintain the mass of glass in the chamber substantiallyconstant; and substantially continuously removing refined molten glassfrom the lower end of the chamber to mainTain the mass of said glasssubstantially constant.
 15. The method set forth in claim 14 wherein thestep of controlling the configuration of the chamber, the speed ofrotation of the chamber, and the amount of glass in the chamber is suchthat the average axial velocity of the glass does not increase from thetop of the mass of glass to the apex of the paraboloidal void.
 16. Themethod set forth in claim 14, including the step of controlling theamount of molten glass in the chamber such that there is a substantialmass of glass between the apex of the paraboloidal void and the outletof the chamber.
 17. The method set forth in claim 16, including the stepof redirecting the molten glass beneath the apex of the paraboloidalvoid so that the molten glass in the area between the void and theoutlet is caused to move radially outward toward the wall of the chamberin advance of the outlet.
 18. The method set forth in claim 16,including the step of redirecting the molten glass beneath the apex ofthe paraboloidal void such that it is caused to move through a pathadjacent the wall of the chamber before moving to the outlet.
 19. Themethod set forth in claim 16, including the step of causing the moltenglass between the apex of the paraboloid void and the outlet to moveradially outward from its axis of rotation and then generally radiallyinward to move portions of the molten glass through an area ofcentrifugal pressure greater than the pressure in the area at the axisof its rotation.
 20. The method set forth in claim 14, including thestep of controlling the speed of rotation of the chamber such that theheight of the paraboloidal void formed in the molten glass is at leastseveral times the maximum diameter of the paraboloidal void.
 21. Themethod set forth in claim 14, wherein the step of controlling the amountof molten glass in the chamber is such that the radial thickness of theglass at the upper end of the chamber exceeds the radius of theparaboloidal void in the glass at the upper end of the chamber.
 22. Themethod set forth in claim 14, wherein the step of introducing moltenglass comprises directing the glass into the open upper end of thechamber laterally such that molten glass merges with the mass of glassin the chamber adjacent the upper end of the chamber.
 23. The method setforth in claim 14, wherein the step of controlling the amount of moltenglass in the chamber is such that the height of the paraboloidal void isabout equal to the depth of glass beneath the apex of the paraboloidalvoid.
 24. The method set forth in claim 14, including the step ofcontrolling the configuration of the chamber such that it has asubstantially constant diameter from the upper end to the lower endthereof.
 25. The method set forth in claim 14, including the step ofcausing the molten glass between the apex of the paraboloidal void andthe outlet to move radially outward from its axis of rotation and thengenerally radially inward to move portions of the molten glass throughan area of centrifugal pressure greater than the pressure in the area atthe axis of its rotation.
 26. The method of refining molten glass whichcomprises: defining a chamber having an axis of rotation; rotating saidchamber about said axis; introducing molten glass, wherein substantiallyall the glass constituents are molten and which contains entrappedgaseous inclusions into the chamber providing a mass of molten glass inthe chamber; continuing the rotating of said chamber about its axis tosubject portions of the mass of glass in the chamber to centrifugalforce, and thereby cause the mass of glass to form a portion of aparaboloidal void under the action of the centrifugal force; andcontrolling the configuration of the chamber, the speed of rotation ofthe chamber, and the amount of glass in the chamber such that at least aportion of the mass of glass in the chamber forms a substantiallycylindrical portion with a paraboloidal voId, said substantiallycylindrical portion of glass extending from the top of the mass of glassin the chamber to the apex of the paraboloidal void, and having a radialthickness which increases progressively from the top to the apex of saidvoid.
 27. The method set forth in claim 26, wherein the step ofcontrolling the amount of molten glass in the chamber is such that theradial thickness of the glass at the upper end of the chamber exceedsthe radius of the paraboloidal void in the glass at the upper end of thechamber.
 28. The method set forth in claim 26, including the step ofcontrolling the configuration of the chamber, such that it has asubstantially constant diameter from the upper end to the lower endthereof.
 29. The method of refining molten glass which comprises:defining a chamber having an axis of rotation and which has a restrictedupper end and a restricted lower end forming an outlet; introducingmolten glass wherein substantially all the glass constituents are moltenand which contains entrapped gaseous inclusions into the open upper endof the chamber providing a mass of molten glass in the chamber; rotatingsaid chamber about its axis to subject portions of the mass of glass inthe chamber to centrifugal force; controlling the configuration of thechamber, the speed of rotation of the chamber, and the amount of glassin the chamber such that a paraboloidal void is formed in the mass ofglass; adding unrefined molten glass to the upper end of the chamber tomaintain the mass of glass in the chamber substantially constant; andsubstantially continuously removing molten glass from the lower end ofthe chamber; and causing the molten glass between the apex of theparaboloidal void and the outlet to move radially outward from its axisof rotation and then generally radially inward to move portions of themolten glass into the area of centrifugal pressure greater than thepressure in the area at the axis of its rotation.